.TH xfs_scrub 8
.SH NAME
xfs_scrub \- check and repair the contents of a mounted XFS filesystem
.SH SYNOPSIS
.B xfs_scrub
[
.B \-abCeMmnpTvx
]
.I mount-point
.br
.B xfs_scrub \-V
.SH DESCRIPTION
.B xfs_scrub
attempts to check and repair all metadata in a mounted XFS filesystem.
.PP
.B WARNING!
This program is
.BR EXPERIMENTAL ","
which means that its behavior and interface
could change at any time!
.PP
.B xfs_scrub
asks the kernel to scrub all metadata objects in the filesystem.
Metadata records are scanned for obviously bad values and then
cross-referenced against other metadata.
The goal is to establish a reasonable confidence about the consistency
of the overall filesystem by examining the consistency of individual
metadata records against the other metadata in the filesystem.
Damaged metadata can be rebuilt from other metadata if there exists
redundant data structures which are intact.
.PP
Filesystem corruption and optimization opportunities will be logged to
the standard error stream.
Enabling verbose mode will increase the amount of status information
sent to the output.
.PP
If the kernel scrub reports that metadata needs repairs or optimizations and
the user does not pass
.B -n
on the command line, this program will ask the kernel to make the repairs and
to perform the optimizations.
See the sections about optimizations and repairs for a list of optimizations
and repairs known to this program.
The kernel may not support repairing or optimizing the filesystem.
If this is the case, the filesystem must be unmounted and
.BR xfs_repair (8)
run on the filesystem to fix the problems.
.SH OPTIONS
.TP
.BI \-a " errors"
Abort if more than this many errors are found on the filesystem.
.TP
.B \-b
Run in background mode.
If the option is specified once, only run a single scrubbing thread at a
time.
If given more than once, an artificial delay of 100us is added to each
scrub call to reduce CPU overhead even further.
.TP
.BI \-C " fd"
This option causes xfs_scrub to write progress information to the
specified file description so that the progress of the filesystem check
can be monitored.
If the file description is a tty, a fancy progress bar is rendered.
Otherwise, a simple numeric status dump compatible with the
.B fsck -C
format is output.
.TP
.B \-e
Specifies what happens when errors are detected.
If
.IR shutdown
is given, the filesystem will be taken offline if errors are found.
If
.IR continue
is given, no action is taken if errors are found; this is the default
behavior.
.TP
.B \-k
Do not call TRIM on the free space.
.TP
.BI \-M " real-mount-point"
Open the this path for issuing scrub system calls to the kernel.
The positional
.I mount-point
parameter will be used for displaying informational messages and logging.
This parameter exists to enable process sandboxing for service mode.
.TP
.BI \-m " file"
Search this file for mounted filesystems instead of /etc/mtab.
.TP
.B \-n
Only check filesystem metadata.
Do not repair or optimize anything.
.HP
.B \-o
.I subopt\c
[\c
.B =\c
.IR value ]
.BR
Override what the program might conclude about the filesystem
if left to its own devices.
.IP
The
.IR subopt ions
supported are:
.RS 1.0i
.TP
.B autofsck
Decide the operating mode from the value of the
.I autofsck
filesystem property.
See the
.B filesystem properties
section for more details.
.TP
.BI fstrim_pct= percentage
To constrain the amount of time spent on fstrim activities during phase 8,
this program tries to balance estimated runtime against completeness of the
trim.
In short, the program avoids small trim requests to save time.

During phase 7, a log-scale histogram of free space extents is constructed.
At the start of phase 8, a CDF is computed in decreasing order of extent
length from the histogram buckets.
A point corresponding to the fstrim percentage target is chosen from the CDF
and mapped back to a histogram bucket.
Free space extents at least as long as the bucket size are trimmed.
Smaller extents are ignored.

By default, the percentage threshold is 99%.
.TP
.BI iwarn
Treat informational messages as warnings.
This will result in a nonzero return code, and a higher logging level.
.RE
.TP
.B \-p
Only optimize filesystem metadata.
If repairs are required, report them and exit.
.TP
.BI \-T
Print timing and memory usage information for each phase.
.TP
.B \-v
Enable verbose mode, which prints periodic status updates.
.TP
.B \-V
Prints the version number and exits.
.TP
.B \-x
Read all file data extents to look for disk errors.
.B xfs_scrub
will issue O_DIRECT reads to the block device directly.
If the block device is a SCSI disk, it will instead issue READ VERIFY commands
directly to the disk.
If media errors are found, the error report will include the disk offset, in
bytes.
If the media errors affect a file, the report will also include the inode
number and file offset, in bytes.
These actions will confirm that all file data blocks can be read from storage.
.SH OPTIMIZATIONS
Optimizations supported by this program include, but are not limited to:
.IP \[bu] 2
Instructing the underlying storage to discard unused extents via the
.B TRIM
ioctl.
.IP \[bu]
Updating secondary superblocks to match the primary superblock.
.IP \[bu]
Turning off shared block write checks for files that no longer share blocks.
.SH REPAIRS
Repairs are performed by calling into the kernel.
This limits the scope of repair activities to rebuilding primary data
structures from secondary data structures, or secondary structures from
primary structures.
The existence of secondary data structures may require features that can
only be turned on from
.BR mkfs.xfs (8).
If errors cannot be repaired, the filesystem must be
unmounted and
.BR xfs_repair (8)
run.
Repairs supported by the kernel include, but are not limited to:
.IP \[bu] 2
Reconstructing extent allocation data.
.IP \[bu]
Rebuilding free space information.
.IP \[bu]
Rebuilding inode indexes.
.IP \[bu]
Fixing minor corruptions of inode records.
.IP \[bu]
Recalculating reference count information.
.IP \[bu]
Reconstructing reverse mapping data from primary extent allocation data.
.IP \[bu]
Scheduling a quotacheck for the next mount.
.PP
If corrupt metadata is successfully repaired, this program will log that
a repair has succeeded instead of a corruption report.
.SH FILESYSTEM PROPERTIES
System administrators can convey their preferences for scrubbing of a
particular filesystem by setting the filesystem property
.B autofsck
via the
.BR xfs_property (8)
command on the filesystem.
These preferences will be honored if the
.B -o autofsck
option is specified.

Recognized values for the
.B autofsck
property are:
.RS
.TP
.I none
Do not scan the filesystem at all.
.TP
.I check
Scan and report corruption and opportunities for optimization, but do not
change anything.
.TP
.I optimize
Scan the filesystem and optimize where possible.
Report corruptions, but do not fix them.
.TP
.I repair
Scan the filesystem, fix corruptions, and optimize where possible.
.RE

If the property is not set, the default is
.I check
if the filesystem has either reverse mapping btrees or parent pointers enabled,
or
.I none
otherwise.

.SH EXIT CODE
The exit code returned by
.B xfs_scrub
is the sum of the following conditions:
.br
\	0\	\-\ No errors
.br
\	1\	\-\ File system errors left uncorrected
.br
\	2\	\-\ File system optimizations possible
.br
\	4\	\-\ Operational error
.br
\	8\	\-\ Usage or syntax error
.br
.SH CAVEATS
.B xfs_scrub
is an immature utility!
Do not run this program unless you have backups of your data!
This program takes advantage of in-kernel scrubbing to verify a given
data structure with locks held and can keep the filesystem busy for a
long time.
The kernel must be new enough to support the SCRUB_METADATA ioctl.
.PP
If errors are found and cannot be repaired, the filesystem must be
unmounted and repaired.
.SH SEE ALSO
.BR xfs_repair (8).
